linux-kernel - [PATCH net v2 1/1] net: phy: microchip: Reset LAN88xx PHY to ensure clean link state on LAN7800/7850

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Message-Id: <20241125084050.414352-1-o.rempel@pengutronix.de>
Date: Mon, 25 Nov 2024 09:40:50 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Andrew Lunn <andrew@...n.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Yuiko Oshino <yuiko.oshino@...rochip.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com,
	Phil Elwell <phil@...pberrypi.org>
Subject: [PATCH net v2 1/1] net: phy: microchip: Reset LAN88xx PHY to ensure clean link state on LAN7800/7850

Fix outdated MII_LPA data in the LAN88xx PHY, which is used in LAN7800
and LAN7850 USB Ethernet controllers. Due to a hardware limitation, the
PHY cannot reliably update link status after parallel detection when the
link partner does not support auto-negotiation. To mitigate this, add a
PHY reset in `lan88xx_link_change_notify()` when `phydev->state` is
`PHY_NOLINK`, ensuring the PHY starts in a clean state and reports
accurate fixed link parallel detection results.

Fixes: 792aec47d59d9 ("add microchip LAN88xx phy driver")
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/net/phy/microchip.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/net/phy/microchip.c b/drivers/net/phy/microchip.c
index d3273bc0da4a..691969a4910f 100644
--- a/drivers/net/phy/microchip.c
+++ b/drivers/net/phy/microchip.c
@@ -351,6 +351,22 @@ static int lan88xx_config_aneg(struct phy_device *phydev)
 static void lan88xx_link_change_notify(struct phy_device *phydev)
 {
 	int temp;
+	int ret;
+
+	/* Reset PHY to ensure MII_LPA provides up-to-date information. This
+	 * issue is reproducible only after parallel detection, as described
+	 * in IEEE 802.3-2022, Section 28.2.3.1 ("Parallel detection function"),
+	 * where the link partner does not support auto-negotiation.
+	 */
+	if (phydev->state == PHY_NOLINK) {
+		ret = phy_init_hw(phydev);
+		if (ret < 0)
+			goto link_change_notify_failed;
+
+		ret = _phy_start_aneg(phydev);
+		if (ret < 0)
+			goto link_change_notify_failed;
+	}
 
 	/* At forced 100 F/H mode, chip may fail to set mode correctly
 	 * when cable is switched between long(~50+m) and short one.
@@ -377,6 +393,11 @@ static void lan88xx_link_change_notify(struct phy_device *phydev)
 		temp |= LAN88XX_INT_MASK_MDINTPIN_EN_;
 		phy_write(phydev, LAN88XX_INT_MASK, temp);
 	}
+
+	return;
+
+link_change_notify_failed:
+	phydev_err(phydev, "Link change process failed %pe\n", ERR_PTR(ret));
 }
 
 /**
-- 
2.39.5